u^ 


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Circular  No.  4,  Second  Series. 

I  oited  States  Department  of  Agriculture, 


DIVISION    OF    KNTOMOLOGY 


THE  ARMY  W 

/  ■ 

01  mi:  \i.    IPPE  \i:  IN(  i:    \m>    mi  i  HO 

In  the  months  of  M.i\   and  June,  and  S< 
wheat,  oats,  and  other  small  grains,  corn, 
blue  grass,  and  other  grasses,  but   seldon 
clover,  are  occasionally  overrun   by   mul 
naked  striped  caterpillars  about  an  inch  a 

let   l«»nir  and    a  quarter  Of  an  inch  in  diaim 

full-grown, rather  dark  in  appearance  and  i 
Bembling  Fig.  1.    '[\wy  usuallj  travel  in  one 
from  one  field  to  another,  destroying  *hecrop  •■; 
go.     They  bav<        abil    >'  - 'n.'e  .   the  stalks 

and  cutting  off  tlu  m<a  by  grass  and  of  the 

small  grains. 

MM  Klltl    I  [ON 

The  army  worm  seems  to  be  an  indigenous  North 
American  insect,  and  <>n  this  continent  is  tnosl 
abundant  in  the  United  States  easl  of  the  Rocky 
Mountains.  Isolated  specimens  have  been  found 
in  KiiL'land  and  South  America,  and  the  moth  has 
been  captured  in  India.  Java,  Australia,  and  V  w 
Zealand.  It  is  nowhere  known  ,-i-  an  especially 
destructive  species,  however,  outside  ol  the  I  oited 
State-.  The  region  iii  which  it  especially  flourishes 
extends  from  eastern  Eowa  to  Maine  and  from 
northern  Texas  to  northern  Alabama.  Easl  of  the 
Bine  Ridge  Mountains  it^  southerly  range  as  an 
injurious  species  extends  only  to  northern  North 
Carolina.  The  moth  i-  often  captured  outside 
these  limit ^  and  frequently  in  considerable  num- 
bers, hut  the  caterpillar  does  not  seem  elsewhere 
to  be  a  factor  in  agriculture. 


ARJIV 


NATURAL    HISTORY    AND    HABITS. 


The  adult  Lnsecl  is  a  brown  moth  with  a  white  spot  on  the  center  of 
each  fore-wing,  as  indicated  at  Fig.  2.  The  eggs  are  very  minute  and 
white  in  color,  round,  and  are  laid  in  strings  of  from  2  or  3  to  15  or  20. 
They  are  pushed  by  the  ovipositor  of  the  female  moth  down  into  the 
inner  base  of  the  terminal  leaf  sheaths  of  grasses  or  grains.  (See  also 
Fig.  2.)  A  strong  effort  is  apparently  made  by  the  female  moth  to 
conceal  them.  They  are  laid  most  abundantly  in  the  thickest  tufts  of 
grass  which  customarily  spring  up  in  pastures  over  spots  where  cattle 
have  dropped.  In  the  vicinity  of  old  fodder  stacks  the  grass  usually 
glows  high,  and  tins  also  is  a  favorite  place  for  egg-laying.  The  moths 
do  not  confine  their  egg-laying  operations  to  such  localities,  however, 

and  the  eggs  have  been  found  in  old 
cornstalks,  thrust  under  the  sheath,  and 
even  under  the  bark  of  old  cedar  posts. 
The  eggs  arc  hatched  in  from  eight 
to  ten  days  and  the  young  caterpillars 
feed  for  a  time  in  the  fold  of  the  leaf, 
growing  rapidly,  and  finally  consum- 
ing entire  leaves. 

Under  ordinary  circumstances,  and 
when  not  present  in  great  numbers, 
the  larvae  feed  mainly  at  night  and  in 
damp  cloudy  weather,  remaining  hid- 
den during  sunshiny  days.  In  this 
respect  they  resemble  in  habits  the 
closely  allied  cutworms.  They  reach 
full  growth  in  three  or  four  weeks,  burrow  into  the  ground,  and 
transform  to  the  brown  pupa?  shown  at  Fig.  2.  In  this  condition 
they  remain  in  the  summer  time  on  an  average  about  two  weeks, 
when  the  moth  again  appears. 

The  number  of  generations  each  year  varies  with  the  climate  and  the 
season.  There  are.  in  the  more  northern  States,  two  or  three  genera- 
tions, and  perhaps  six  in  the  more  southern  States. 

We  have  said  above  that  the  insect  normally  feeds  by  night  and 
hides  by  day.  and  to  this  habit  is  due  the  fact  that,  although  the  army 
worm  is  present  every  year  all  through  the  region  especially  indicated 
in  a  previous  paragraph,  it  is  only  noticed  when  it  becomes  excessively 
abundant,  and  this  occurs  usually  only  at  intervals  of  several  years. 

With  a  favorable  succession  of  seasons  the  insect  multiplies  in  geo- 
metrical ratio,  and  at  last  becomes  so  numerous  as  to  necessitate  migra- 
tion for  food.  It  then  travels  and  feeds  during  both  day  and  night, 
and  it  is  then  that  the  insect  becomes  very  injurious  and  that  reports 
of  great  damage  are  heard. 

The  insect  passes  the  winter  normally, as  do  most  of  the  related  cut- 
worms, in  the  half-grown  caterpillar  or  larval  condition.     In  the  South 


Fig.  2.— The  Army  Worm  {Leucania  uni- 
puncta  :  Moth  above,  pupa  below,  and 
eggs  in  natural  position  in  a  grass  leaf 
all  natural  size,     i  From  Comstock.) 


8 

it  also  undoubtedly  hibernates  a  .1  moth,  and  there  i-  some  evidence 
thai  it  ma)  pass  the  winter  occasionally,  although  exceptionally,  in 
the  egg  state. 

The  injurious  brood  ma)  be  the  first,  second,  or  third.  The  over- 
wintered larvse  maj  occasionally  be  so  abundanl  as  to  attract  notice, 
hut  in  the  majority  of  cases  it  is  the  offspring  of  these  overwintered 
indiN  iduals  w  Inch  cause  alarm. 

In  general  it  ma)  be  said  that  the  worms  arc  more  apl  to  make  an 
injurious  appearance  in  a  rain)  spring  or  earl)  summer  following  a 
Beason  of  comparative  drouth.  The  presenl  season  (1894  bears  out 
these  conditions  in  the  Eastern  States,  and  a-  a  matter  of  fact  the 
arm)  worm  has  been  more  abundanl  in  certain  eastern  sections  than 
it  has  been  since  1888. 

REM]  DIES     Wl»    PEE\  I.N  I  i\  I.    ME  \-i  RES. 

There  is  never  an)  demand  upon  this  office  i"i  remedies  for  the 
army  worm  until  it  i>  almost  too  late  t<>  do  an)  immediate  good. 
The  re  arc  certain  old-time  measures  which  ma)  he  adopted  to  protect 
certain  licit  I  -  from  advancing  armies,  like  t  he  plowing  of  a  furrow  with 
its  perpendicular  side  toward  the  field  to  he  protected  and  the  subse- 
quent dragging  of  a  log  through  the  furrow  to  keep  the  earth  friable 
and  kill  the  worms  which  have  accumulated  in  the  ditch,  and  another 
is  the  sprinkling  of  a  -.trip  n(  pasture  or  field  crop  in  advance  of  an 
army  with  Paris  green  or  London  purple  in  solution.  In  fields  which 
the  caterpillars  have  already  entered  there  i-  little  which  can  be  done 
for  their  destruction  which  does  not  also  involve  th<  destruction  of  the 
crop.  The  fields  may  he  sprinkled  by  mean-  of  a  broadcast  sprayer 
with  an  arsenical  solution,  or  they  may  he  rolled  with  a  heav\  roller 
where  one  i-  at  hand  and  the  ground  is  level,  or  a  flock  of  sheep  ma)  he 
sent  in,  which  will  result  in  crushing  most  of  the  worm-  b)  trampling. 

In  the  great  majority  of  cases,  however,  these  latter  measures  arc 
unnecessary,  for  the  reason  that  nature  herself  almost  always  take-  a 
hand  in  the  red  net  ion  of  t  he  excessive  cumbers  of  the  insect,  either  by 
unfavorable  weather  conditions  or  by  the  excessive  multiplication  of 
natural  enemies  and  parasites,  so  that  it  i-  extremely  rarely  that  we 
hear  of  one  army-w  orm  outbreak  immediately  following  another. 

In  general,  therefore,  it  may  he  -aid  that,  a-  soon  a-  the  worm-  are 
discovered  to  he  exceptionally  numerous  in  a  given  held  (and  a-  a 
matter  of  fact,  they  are  at  first  almost  invariably  restricted  to  the 
immediate  neighborhood  of  some  definitely  limited,  permanent  breed- 
ing place  I,  all  energies  should  he  devoted  to  the  protection  of  the  sur- 
rounding crops  by  the  means  mentioned  above,  and  the  destruction 
of  the  worms  in  the  fields  first  attacked  may  he  safely  left  to  the  last. 

There  are  many  localities  in  w  Inch  the  army  worm  i-  never  -ecu.  or, 
rather,  is  never  known  to  ho  injurious,  and  these  localities  owe  their 
exemption  undoubtedly  to  the  unconscious  use  of  preventive  meas- 


ures.  Clean  cultivation,  rotation  of  crops,  cleaning  up  fence  corners, 
close  pasturage,  the  burning  over  of  waste  grass  land  in  spring  or  fall 
arc  all  preventive  measures  of  great  value,  since,  where  these  methods 
are  in  vogue,  the  army  worm  will  never  he  able  to  get  a  migratory- 
start,  or,  in  other  words,  it  never  becomes  so  abundant  as  to  necessi- 
tate migration. 

Bearing  in  mind  the  fact  that  the  insect  breeds  normally  in  rank 
grass,  such  as  is  usually  found  along  the  edges  of  swamps  (not  in 
swamps,  for  the  insect  must  have  comparatively  dry  earth  in  which  to 
pupate)  or  in  accidentally  overfertilized  spots  in  pasture  lands,  and 
that  it  feeds  normally  only  upon  true  grasses,  the  farmer  who  has 
once  suffered  from  army-worm  attack  may  easily  prevent  its  recur- 
rence by  winter  burning  or  by  rotation  and  clean  cultivation. 

In  cases  where  the  worms  have  already  entered  a  valuable  field  of 
wheat  before  the  farmer  has  become  aware  of  their  presence,  and  too 
late  to  render  ditching  of  any  avail,  some  little  good  may  be  accom- 
plished if  the  majority  of  the  worms  are  full  grown,  or  nearly  full 
grown,  by  the  old  method  of  "dragging  the  rope."  Two  men,  each 
having  hold  of  the  end  of  a  long  rope,  are  sent  through  the  field  and 
the  rope  is  dragged  over  the  heads  of  the  grain.  The  backward  jerk 
of  the  stalks  jars  the  caterpillars  to  the  ground,  and  they  are  unable  to 
ascend  to  the  heads  again  for  some  little  time.  This  is  a  laborious 
process,  however,  and  has  to  be  repeated  almost  immediately.  It  is 
only  to  be  undertaken  where  the  number  of  worms  in  a  field  is  com- 
paratively small  and  where  these  are,  as  before  stated,  full  grown  or 
nearly  full  grown,  since  in  this  case  they  will  stop  feeding  and  enter  the 
ground  in  a  day  or  two. 

NATURAL    ENEMIES. 

There  is  almost  no  prominent  injurious  insect  in  whose  economy 
natural  enemies  play  a  more  important  part  than  the  army  worm.  We 
have  said  above  that  in  the  great  majority  of  cases  actual  destructive 
measures  against  army  worms  which  have  once  taken  full  possession 
of  a  grass  field  are  hardly  necessary.  This  is  because  of  the  fact  that 
generally  not  more  than  one  worm  out  of  a  thousand  escapes  death 
from  parasitic  or  predaceous  insects.  Where  the  army  worm  follows 
its  normal  habit  and  feeds  only  at  night,  remaining  hidden  during  the 
day  under  the  surface  of  the  ground  at  the  base  of  some  tuft  of  rank- 
growing  grass,  it  is  protected  from  these  natural  enemies,  but  when  the 
migratory  instinct  drives  it  forth  and  perverts  its  normal  habit,  caus- 
ing it  to  march  unprotected  during  the  day.  the  swift-breeding  tachina 
Hies  attack  it  at  once,  multiply  most  rapidly,  and  in  connection  with 
1 1 -^  other  parasites  and  with  the  predatory  ground-beetles,  reduce  its 
numbers  once  more  to  the  noninjurious  point.  We  have  said  this  is 
generally  the  case:  then1  may  he  exceptions,  but  we  have  never  seen 
"lie.      ft  is  important,  however,  for  the  farmer  to  be  able  to  recognize 


ire 


;  Ml  I  I.  I    V  m\  v- 

i  LI .  writ] 
pup 

of  mi  Army 
\\  onn  with  I  u 

rhal  onlargi 


Reappearance  of  a  parasitized  worn,  asm  this  wa3  his  confidence  in 

the  ful  ure  max  be  restored 

\\,.  3hoM  ai  Fig.  3  the  head  and  from  segments  ol  an  arm)   worm 
tearing  eg*rs  of  the  red-tailed   tachina  ll>    ^  Vemoriea  leucm 
eggs  are  white,  oval,  less  than  one-sixteenth  ol  an  inch  long,  and 
glued    fast    to   the  skin   of   the  caterpillar, 
usuallj  on  the  back  .-I'  the  fronl  segments. 
From  half  a  dozen  to  fifty  or  more  of  these 
eggs  uuw  be  attached  to  a  single  caterpillar, 
and  from  each  hatches  a  maggol  which  pene 
trates  the  bod}  of  the  arm>  worm  and  ulti- 
mately  destroys    it,  unless    the    caterpillar 
should  happen  to  casl  its  skin  so  soon  after 
the  eggs  are  laid  thai  thej  do  uol  have  tunc 
to  hatch.     The  adull  tachina-fl}  resembles 
a  rather  large  house-fly,  except   that  il  has 
B  red  tip  to  its  abdomen.     Hundreds  and 
thousands  of   these    flies   are   usually    seen 
buzzing  aboul  a  field  infested  1>>  the  arm3  worm,  and  theirpresence 
should  be  welcome  to  the  fanner. 

The  extenl  of  the  parasitism  of  the  injurious  br I  ol  the  armj 

worm  may  be  indicated  b3  two  instances  from  our  personal  experience. 
In  1880  we  visited  a  large  tract  of  land  planted  in  timothy  grass  ... 
the  vicinitv  of  Portsmouth,  Va.  A  search  for  hours  during  the  hot 
partoftheda^  failed  to  show  a  single  worm  which  did  not  bear  tachina 

a      i„  ,ss-  xx,.  visited  wheat  fields  in  the  vicinity  ol  HuntsviUe, 

S  which  were  then  being  overrun  b3  this  insect.  Here,  although  a 
Qum'ber  of  worms  were  noticed  which  did  nol  bear  tachina  eggs,  they 
were  destroyed  b3  ground-beetles  to  such  an  extent  that  when  we 
attempted  to  catch  an  adult  moth  a  little  later  in  the  season  b3  means 
of  trap  lanterns  and  sugar,  we  were  unable  to  secure  a  single  specimen. 
The  entire  army  had  been  amuhilated,  and  i1  is  worthy  ol  remark  tnal 
1U  neither  of  these  localities  has  the  army  worm  ever  been  seen  since 
m  injurious  numbers,  although  fourteen  years  have  elapsed  in  the  one 
case  and  twelve  in  the  other. 


1..  (  >.  lloxx  \i:i>. 

Entomologist. 


Approved : 

.1.  Sterling  M«>k roN, 

Secrt  tary. 

\\  ilshinoton,  l>  C,  •/'""  16, 


O 


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UNIVERSITY  OF  FLORIDA 


3  1262  09216  5918 


